The Steamboating Forum

A mild superheat works fine as our small engines tend to suffer from a lot of condensation... but 600F is a real PITA. It means bronze valves won't do, rope is right out for insulation, and any lube oil will oxidize very quickly. You cannot use any o-rings, teflon packing is out, etc.

For 600F I'd use poppet valves and a very short cut-off to make effective use of all that heat. You also want a very well
lagged (insulated) engine since high temps mean more losses.

With that much superheater surface, designing a superheater that won't burn up when firing up (no steam flow) is a real trick.

I would NOT do this on my first steamboat.

- Bart

The issue is I plan on having a woodfired monotube boiler. In order to control it, i'm going to have to have some amount of superheat built in so that I can make sure i'm actually pumping steam through the thing instead of hot water. i.e. if I have a 125 PSI safety, and the exhaust temperature is 350 F, then i know I must be producing steam...

How much superheat can I safely run on something like the M-Compound, with steam oil? Best guesses welcome...

--Steve

Depends which steam oil you pick. There are some for no s/heat, low s/heat or higher s/heat etc.

If I were looking at this, I'd seriously consider a design that utilizes a dynamic steam trap to bleed extra water from the coil perhaps 2/3 of the way along; you can then adjust the feed water pump displacement to maintain some flow of water from the trap. This will help you prevent excessive temperatures.

I'd also consider using a relief valve set at a higher pressure than you plan to operate by a good bit; since you don't have a drum this is easy enough.

Also check out http://www.steamboat.com.au/SL%20ALBA.doc

- Bart

barts wrote: With that much superheater surface, designing a superheater that won't burn up when firing up (no steam flow) is a real trick.

I would NOT do this on my first steamboat.

- Bart

The whole design is that there is always water travelling through the coil though. There will be a 15 sq ft heat exchanger to take waste steam from the boiler and the engine and use it to heat the feed water. Excess water / steam goes overboard.

When firing up, the first step is to turn the water pump on (electric) and set to a low level. Then you build your fire, let it get started, then let the microcontroller take over firing, managing air flow through the firebox. It will then adjust the air flow such that the output steam is at 'x' temperature, where 'x' is superheated. Once the fire is going, this really shouldn't take long. There's only about a cup of water in the entire boiler, so there's not much to heat. Then you slowly adjust the valving after the boiler to start sending a bit of steam to the engine to warm the engine. There is still some steam going through the feedwater heater at this point. Your boiler is still producing steam at a set temperature.

Once the engine is warm, you can slowly close off the valving to the feedwater heater. This slowly raises the pressure in the boiler, and the fans adjust their firing rate to compensate. Once the pressure builds enough, the engine picks up speed, and away you go!

Now, you can control the entire operation by changing the speed of the water pump. The water pump rate is your throttle. You ramp up the rate of water going through the boiler, the fans ramp up their rate of firing, and they continue to produce steam at the set temperature.

I need superheat because I need enough of a margin of error for the fans to adjust the firing rate when you change the throttle. I can improve things somewhat using a smith predictor to predict required fan speed, then let the controller fine tune, but even then the prediction isn't going to be perfect.

As for lagging: The plan is to insulate the firebox and steamlines with high temperature insulation of the type found inside electric kilns. You can buy a roll of 50' of the stuff, and it's rated to 2000F.

I really feel I should move this into it's own thread, as this has no correlation to the Tiny Power M anymore!

--Steve

Sounds like a very ambitious plan. You might want to communicate with the folks over at the SACA (SteamAutomobileClubofAmerica)forum as well. They have lots of experience with those types of set ups for steam cars.

-Ron

Hope to see an article soon.

Ron Fossum

DetroiTug wrote:In the "Archives" section of this forum, there is a thread titled "1958 Tiny Power Twin". It's from the old forum. It's basically the same as a single. The thread is not very complete, I took a bunch of pictures and was going to do a Steamboating Magazine article on the build, and my PC hard drive crashed. I learned the hard way, install a second drive and back everything up to it.

They are really good engines, powerful and very strongly built.

-Ron

artemis wrote:Hope to see an article soon.

Ron Fossum

There already is an article of this control system. It's simply the design that the Vital Byte uses, scaled up from a model, to a full sized boat! Well... the power plant is scaled up a bit. The electronics are essentially the same. This does have an impact on the controller as it changes the impulse response of the system.

flashtwo, the creator of the system discusses it on this very forum! http://www.thesteamboatingforum.net/for ... ?f=8&t=675

To my knowledge, no one has applied the system to a full sized boat yet. I'm a computer engineer, so the thought of tinkering with the code to make it work JUST RIGHT is exciting... A mix of the old with the new... Though, I understand, not everybody's cup of tea...

See the Vital Byte in action here:

http://www.youtube.com/watch?v=_gataEIamQk

--Steve